1. Field of the Invention
The invention relates to a dosing valve that may be used for dosing a liquid from a pressurized accumulator.
2. Detailed Description of Prior Art
The dosing valve is suitable in particular for dosing a liquid additive that is at risk of freezing. Such a liquid additive that is at risk of freezing is for example a urea-water solution. A urea-water solution is generally used for exhaust-gas purification in exhaust-gas treatment devices in the automotive field. In recent times, in exhaust-gas treatment devices for the purification of the exhaust gases of internal combustion engines in motor vehicles, increasing use has been made of the SCR [Selective Catalytic Reduction] method. In said method, nitrogen oxide compounds in the exhaust gas are reduced to form non-hazardous substances. For this purpose, urea-water solution as reducing agent precursor, or ammonia as reducing agent, is fed to the exhaust-gas treatment device. The urea-water solution is converted to form ammonia thermolytically (by high temperatures) and/or hydrolytically (with assistance from a catalytic converter). The nitrogen oxide compounds in the exhaust gas react with the ammonia to form non-hazardous substances (in particular to form CO2, water and nitrogen). The additive is for example urea-water solution.
For exhaust-gas purification, widespread use is made of a 32.5% urea-water solution that is available under the trade name AdBlue®. Said urea-water solution freezes at −11° C. In the automotive field, such low temperatures can arise in particular during long standstill phases.
An SCR dosing system may be designed such that, even during said standstill phases, liquid additive is present in a dosing valve provided for dosing the liquid additive. The SCR dosing system is thus not evacuated in the event of a shutdown. The SCR dosing system must therefore be configured such that it is not damaged as a result of freezing of the reducing agent. Nevertheless, all of the components of the SCR dosing system, in particular the dosing valve, should at the same time be as inexpensive as possible.